JP2004252266A - Electrifying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying device having such structure that electrification is performed by maintaining a very small gap between the electrifying device and a latent image carrier and the gap is surely accurately maintained to prevent adverse effect such as abnormal discharge. <P>SOLUTION: The electrifying device 27M using an electrifying roller where a material layer 27M2 capable of being electrified is formed on the circumferential surface of a core bar 27M1 and which is provided with a gap holding member that forms a gap by being wound on the surface of the material layer 27M2 capable of being electrified and projected from the surface of the material layer 27M2 to come in contact with the other side, is characterised in that a part 27M3 being a part of the surface of the material layer 27M2 capable of being electrified forms a groove 27P as a slippage preventive part or is constituted to have different surface roughness. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging device and an image forming apparatus, and more particularly, to a configuration for maintaining a predetermined gap set between the charging device and a latent image carrier.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine, an electrostatic latent image corresponding to image information from an exposure scan or a host computer is formed on a latent image carrier, and the electrostatic latent image is formed. There is a method in which a visible image is transferred to a recording medium such as a sheet after the visible image processing, and the transferred image is fixed to produce a copy or printout.
[0003]
The latent image carrier is charged uniformly on the surface of the photosensitive layer prior to the formation of the electrostatic latent image. The non-contact charging system using a corona charger or the like and a charging roller are used in the charging process. 2. Description of the Related Art A contact charging system capable of injecting electric charge by contacting an image carrier is known.
[0004]
The contact charging method uses a charging roller having a structure in which an elastic layer and a high-resistance layer are sequentially laminated on the surface of a core metal, and charges the latent image carrier surface by applying a predetermined voltage to the core metal. It tends to be used frequently in recent years because discharge products such as ozone and nitrogen oxide (NOx), which are observed in the non-contact charging system, are not generated and no adverse effects on the environment are caused.
However, in the contact charging method, since the charging roller serving as a charging member is in direct contact with the latent image carrier, foreign matters such as toner and paper powder remaining on the latent image carrier are likely to adhere. This may cause uneven charging of the latent image carrier.
[0005]
Therefore, there is a non-contact charging system in which a minute gap, that is, a so-called gap is set between the latent image carrier and the charging roller, and a discharge is performed in the minute gap. A structure in which a film is wound on the outer peripheral surface on the side of the direction end to set the minute gap described above (for example, Patent Document 1), a step or a groove is provided at an end in the axial direction of the charging roller, and a gap holding member is provided there. A configuration in which a charging roller is loaded is known (for example, Patent Literature 2), and a configuration in which a resin is provided on the outer peripheral surface of a cored bar instead of an elastic body is known as a configuration of a charging roller (for example, Patent Literature 3). ).
[0006]
[Patent Document 1]
JP 2001-194868 A (paragraph “0038” column, FIG. 4)
[Patent Document 2]
JP-A-2002-55508 (paragraph “0018” column, FIG. 5)
[Patent Document 3]
JP 2001-337515 A (paragraph “0020” column, FIG. 1)
[0007]
[Problems to be solved by the invention]
When rubber is used as the elastic member used in the configuration of the charging roller, it is difficult to perform high-precision cutting, and, due to the member having a large thermal expansion, depending on the use environment. The gap maintaining accuracy is extremely poor.
On the other hand, when a resin material is used in place of the elastic material, the processing accuracy can be easily obtained because the hardness is stable and the processing is easy. In such a case, the gap accuracy may not be maintained due to abrasion due to rubbing over time. When an organic photoreceptor is used as the latent image carrier, the surface of the photoreceptor may be damaged by the contact of a gap holding member having a higher hardness than the photoreceptor material.
[0008]
Considering the wear of the material used for the gap holding member for the purpose of maintaining the gap accuracy, it is also conceivable to provide a thicker film than the film and provide it on the surface of the charging roller. As described above, the gap holding member may be provided at the step of the charging roller and held so as not to come off.
[0009]
However, when the gap holding member is mounted on the charging roller, slipping between the charging roller and the charging roller, in other words, rotation due to frictional relationship is not suppressed. For this reason, if slippage occurs between the charging roller and the gap holding member over time, the gap holding member thermally expands, thereby changing the size of the gap due to a dimensional change in the thickness direction of the gap member. become. In particular, when the thickness increases due to thermal expansion, the gap becomes larger than a predetermined value, and abnormal discharge may occur. The abnormal discharge cannot obtain uniform charging, and not only uneven charging and destruction of the photosensitive layer, but also an image having a formed image density and gradation that differ from desired conditions can be obtained.
[0010]
An object of the present invention is to target the above-described conventional charging device, particularly a configuration in which charging is performed while maintaining a small gap between the charging device and a latent image carrier, and reliably maintain gap accuracy to prevent adverse effects such as abnormal discharge. It is an object of the present invention to provide a charging device and an image forming apparatus having a configuration capable of performing the following operations.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, a chargeable material layer is formed on the outer peripheral surface of the cored bar, and the chargeable material layer is wound on the surface of the chargeable material layer, protrudes from the surface of the material layer, and comes into contact with a mating side. In the charging device using the charging roller provided with the gap holding member capable of forming the above, a part of the surface of the chargeable material layer is configured as a non-slip portion.
[0012]
According to a second aspect of the present invention, in addition to the first aspect, the non-slip portion includes at least a region where the gap holding member is located.
[0013]
According to a third aspect of the present invention, in addition to the first or second aspect, the surface roughness of a part of the surface of the material layer where the gap holding member is located is made larger than the surface of the material layer. It is characterized by having.
[0014]
According to a fourth aspect of the present invention, in addition to the first aspect, a resin material containing an ion conductive material is used for the chargeable material layer. Features.
[0015]
According to a fifth aspect of the present invention, in addition to the first aspect of the present invention, the gap holding member is made of an insulating material containing fluorine.
[0016]
According to a sixth aspect of the present invention, in addition to the first aspect of the present invention, a part of the material layer where the gap holding member is located is parallel to a longitudinal direction of the cored bar. It is characterized in that a plurality of grooves having a depth of 10 to 1000 (μm) are formed.
[0017]
According to a seventh aspect of the present invention, in addition to one of the first to fifth aspects, a part of the material layer where the gap holding member is located is provided on a part of the material layer with respect to a longitudinal direction of the cored bar. It is characterized in that a plurality of grooves having a tilt angle and a depth of 10 to 1000 (μm) are formed.
[0018]
The invention according to claim 8 uses the charging device according to any one of claims 1 to 7 for an image forming apparatus, wherein a gap between the gap holding member and the latent image carrier is set to 100 μm or less. It is characterized by having.
[0019]
According to a ninth aspect of the present invention, in addition to the eighth aspect of the present invention, the charging device has a peak-to-peak voltage that is at least twice the discharge starting voltage between the chargeable material layer and the latent image carrier. It is characterized in that the charging process is performed by superimposing and applying an AC voltage.
[0020]
According to a tenth aspect of the present invention, in addition to the eighth or ninth aspect, the charging device includes a cleaning member for cleaning the chargeable material layer, and the cleaning member is provided in a width direction of the material layer. And a structure capable of forming a layer including the gap holding member.
[0021]
According to an eleventh aspect of the present invention, in addition to the invention of the eighth aspect, at least the latent image carrier and the charging device are collectively housed to form a unit structure. A process cartridge is provided which is detachable from a housing in which the carrier and the charging device are arranged.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the illustrated examples.
FIG. 1 is a diagram showing one of the image forming apparatuses to which the belt device according to the present embodiment is applied, and the embodiments of the invention according to claims 14 to 16 will be described below.
The image forming apparatus shown in FIG. 1 uses a copying machine or a printer capable of forming a full-color image by the above-described four-tandem tandem system.
Other image forming apparatuses include a facsimile apparatus capable of performing image forming processing similar to that of the above-described copier and printer based on a received image signal. It should be noted that the image forming apparatus includes not only the above-described color image but also an apparatus which targets a single color image.
[0023]
The image forming apparatus 20 shown in FIG. 1 forms a color image directly from a latent image carrier on a recording sheet by superimposing and transferring an image for each color separation onto a recording sheet such as paper adsorbed on a transfer belt used as a transfer body. Is used.
[0024]
In FIG. 1, the image forming apparatus 20 includes the following devices.
An image forming apparatus 21M, 21C, 21Y, 21BK for forming an image for each color according to a document image, a transfer apparatus 22 arranged opposite to each image forming apparatus 21M, 21C, 21Y, 21BK, and each image forming The manual feed tray 23 serving as a sheet supply unit that supplies a recording sheet to a transfer area where the devices 21M, 21C, 21Y, and 21BK and the transfer device 22 face each other, a first paper feed cassette 24A provided in a paper feed device 24, (2) a paper feed cassette 24B, a registration roller 30 for supplying the recording sheet conveyed from the manual feed tray 23 and the paper feed cassettes 24, 24 in accordance with the image forming timing by the image forming apparatuses 21M, 21C, 21Y, 21BK; This is a fixing device 1 for fixing a sheet-like medium after transfer in a transfer area. Although not described in detail, the fixing device 1 is configured to adopt a belt fixing method in which a heated belt is disposed on a side facing an image. For this reason, the fixing device 1 is equipped with a heat source for heating the belt and a fixing roller and a pressure roller constituting a nip portion which is a fixing area while nipping and conveying the sheet opposite to the belt. It is configured such that it is hung between a roller and a heat source and passes through the nip.
[0025]
The transfer device 22 uses a belt (hereinafter, referred to as a transfer belt) 22A wrapped around a plurality of rollers as a transfer body. The details will be described with reference to FIG. Transfer bias means 22M, 22C, 22Y, and 22BK for applying a transfer bias are disposed at opposing positions, and the first color is transferred in the moving direction of the transfer belt 22A (the direction indicated by the arrow in FIG. 1). At the side, an attraction bias means 31 for applying an attraction bias for attracting the recording sheet to the transfer belt 22A prior to the transfer of the first color is disposed so as to be able to abut the transfer belt 22A.
The transfer belt 22A used in the transfer device 22 in the present embodiment is formed by molding a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, polyethylene terephthalate, etc. into a seamless belt. These transfer belt materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. In addition, a surface layer may be formed by using a method such as spraying or dipping using these resins as a base layer to form a laminated structure.
[0026]
The image forming apparatus 20 includes plain paper generally used for copying and the like, 90K paper such as an OHP sheet, a card, and a postcard, and a basis weight of about 100 g / m. ² It is possible to use any of a considerable amount of thick paper and a so-called special sheet having a larger heat capacity than paper, such as an envelope, as the recording sheet.
[0027]
FIG. 2 is a diagram showing details of each image forming apparatus. Each of the image forming apparatuses 21M, 21C, 21Y, and 21BK performs development of each color of magenta, cyan, yellow, and black. Although the colors are different, since the configurations are the same, the configuration of the imaging device 21M will be described as a representative of the imaging devices 21M, 21C, 21Y, and 21BK.
The image forming device 21M includes a photosensitive drum 25M as an electrostatic latent image carrier, a charging device 27M arranged in order along the rotation direction (clockwise in the configuration shown in FIG. 2) of the photosensitive drum 25M, and a developing device. 26M, a cleaning device 28M, and an electrostatic latent image is formed between the charging device 27M and the developing device 26M in accordance with image information corresponding to a color separated by a writing light 29M from the writing device 29. Is used. The electrostatic latent image carrier may be in the form of a belt instead of the drum.
[0028]
In the image forming apparatus 20 having the above configuration, image formation is performed based on the following steps and conditions. In the following description, an image forming apparatus that forms an image using magenta toner indicated by reference numeral 21M as a representative of each image forming apparatus will be described. However, the same applies to other image forming apparatuses. Is put in front.
At the time of image formation, the photoconductor drum 25M is driven to rotate by a main motor (not shown), is discharged by an AC bias (DC component is zero) applied to the charging device 27M, and its surface potential is set to a reference potential.
Next, the photosensitive drum 25M is uniformly charged to a potential substantially equal to a DC component by applying a DC bias in which an AC bias that is twice or more the discharge start voltage is superimposed on the charging device 27M. The potential is charged to a target charging potential set by the image forming process control unit.
[0029]
When the photosensitive drum 25M is uniformly charged, a writing process is executed. The image to be written is written for forming an electrostatic latent image by using the writing device 29 in accordance with digital image information from a controller (not shown). That is, in the writing device 29, laser light from a laser light source that emits light based on a laser diode light emission signal binarized for each color in accordance with digital image information is supplied to a cylinder lens (not shown), a polygon motor 29A, A photosensitive drum carrying an image for each color, in this case, for convenience, is irradiated onto a photosensitive drum 25M via an fθ lens (not shown), first to third mirrors, and a WTL lens. The surface potential on the surface of the photoconductor drum in the portion thus set becomes substantially the reference potential, and an electrostatic latent image corresponding to the image information is formed.
[0030]
The electrostatic latent image formed on the photoreceptor drum 25M is subjected to visible image processing by a developing device 26M using toner of a color complementary to the color separation color. Is applied, the toner (negative polarity) is developed only in the image portion whose potential has been reduced by the irradiation of the writing light, and a toner image is formed.
[0031]
The toner image of each color subjected to the visible image processing in the developing process becomes a child transferred to a recording sheet that is fed out with registration timing set by the registration roller 30, but before the recording sheet reaches the transfer belt 22A. The sheet is attracted electrostatically to the transfer belt 22A by application of an attraction bias by a sheet attraction bias means 31 composed of a roller.
A recording sheet which is electrostatically attracted to the transfer belt 22A and is conveyed and moved together with the transfer belt 22A (for convenience, indicated by reference numeral S in FIG. 2) is provided in the transfer device 22 at a position facing the photosensitive drum in each image forming apparatus. The toner image is electrostatically transferred from the photosensitive drum by applying a bias having a polarity opposite to that of the toner by the transfer bias units 22M, 22C, 22Y, and 22BK.
[0032]
The transfer paper that has undergone the transfer process for each color is separated from the transfer belt 22A by a drive roller of the transfer belt unit (for convenience, indicated by reference numeral 22A1 in FIG. 2), and is conveyed toward the fixing device 1 (see FIG. 1). The toner image is fixed on the transfer paper by passing through a fixing nip constituted by a fixing belt and a pressure roller. Thereafter, in the case of single-sided printing, the internal discharge tray 32 (see FIG. 1), Alternatively, the paper is discharged to the external paper discharge tray 33 (see FIG. 1).
[0033]
The image forming apparatus 20 shown in FIG. 1 has a configuration capable of forming images on both sides of a recording sheet.
In FIG. 1, a recording sheet S that has passed through the fixing device 1 is conveyed toward a double-side reversing unit 34 when the double-sided image forming mode is selected in advance, and inside the unit 34, the first surface and the second surface Are turned over, and then transported to the duplex transport unit 35. The recording sheet S conveyed from the double-sided conveyance unit 35 is conveyed toward the registration roller 30 and fed out to the transfer position, as in the case of forming an image on one side. The recording sheet S that has passed the fixing device 1 after the image formation on the first surface and the second surface of the recording sheet S has been completed is discharged to one of the paper discharge units in the same manner as when forming the image on one surface. . In FIG. 2, reference numeral 36 indicates a cleaning device for the transfer belt 22A.
[0034]
The transfer belt 22A provided in the transfer device 22 is wrapped around a plurality of rollers including the drive roller 22A1, and forms a spread surface facing each image forming unit. Further, when forming a monochrome image instead of a full-color image, the transfer belt 22A faces the sheet only to the black image forming section 21BK and uses a non-black sheet so that the sheet does not face the image forming section other than black. (In a state shown by a two-dot chain line in FIG. 1).
[0035]
Details of the photosensitive drum, charging device, developing device, and cleaning device used in each image forming device in the image forming apparatus 20 as described above will be described. It should be noted that the configuration related to the setting of the gap between the charging device and the photosensitive drum will be described later in detail.
In the present embodiment, the photoconductor drums 25M, 25Y, 25C, and 25Bk are set to have an outer diameter of φ30 mm and move at 125 mm / sec. The structure of the photoconductor drum is such that an undercoat layer, a charge generation layer mainly composed of a charge generation material, and a charge transport layer mainly composed of a charge transport material are laminated on a conductive support. .
[0036]
The conductive support has a volume resistance of 10 ⁴ A material having a conductivity of Ωcm or less, for example, a metal tube such as aluminum or stainless steel, or a metal such as nickel processed into an endless belt shape is used.
The undercoat layer generally contains a resin as a main component. However, considering that the photosensitive layer is coated thereon with a solvent, these resins are resins having high solubility resistance to general organic solvents. Is desirable. Examples of such a resin include a water-soluble resin such as a polyvinyl alcohol resin, an alcohol-soluble resin such as a copolymerized nylon, a polyurethane resin, an alkyd-melamine resin, and an epoxy resin, and a curable resin that forms a three-dimensional network structure. No. Further, fine powder of a metal oxide such as titanium oxide, silica, and alumina may be added to the undercoat layer in order to prevent moiré and reduce residual potential. This undercoat layer can be formed using an appropriate solvent and a coating method. The thickness of the undercoat layer is suitably from 0 to 5 μm.
[0037]
The charge generation layer is a layer containing a charge generation material as a main component, and typical examples are a monoazo pigment, a disazo pigment, a trisazo pigment, and a phthalocyanine pigment. The charge generation material can be formed by dispersing the charge generation material together with a binder resin such as polycarbonate using a solvent such as tetrahydrofuran or cyclohexanone, and applying a dispersion. The coating is performed by a dip coating method or a spray coating. The thickness of the charge generation layer is usually 0.01 to 5 μm.
[0038]
The charge transporting layer can be formed by dissolving or dispersing the charge transporting material and the binder resin in an appropriate solvent of tetrahydrofuran, toluene, and dichloroethane, and applying and drying this. Among the charge transport materials, low-molecular charge transport materials include an electron transport material and a hole transport material. Examples of the electron transporting material include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, Electron accepting substances such as 3,7-trinitrodibenzothiophene-5,5-dioxide are exemplified. Examples of the hole transport material include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, thiophene derivatives, and the like. Electron donating substances. As the binder resin used for the charge transport layer together with the charge transport material, polystyrene resin, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, polyester resin, polyarylate resin, polycarbonate resin, acrylic resin, epoxy resin, melamine Thermoplastic or thermosetting resins such as resin and phenolic resin are exemplified. The thickness of the charge transport layer may be appropriately selected in the range of 5 to 30 μm according to desired characteristics of the photoreceptor.
[0039]
Further, a protective layer may be formed on the photoreceptor as a surface layer for the purpose of protecting the photosensitive layer and improving durability.
[0040]
In the charging devices 27M, 27Y, 27C, and 27Bk, an insulating resin (for convenience, indicated by reference numeral 27M2 in FIG. 2) is disposed as a chargeable material layer on the outer peripheral surface of a cored bar (for convenience, indicated by reference numeral 27M1). As will be described later, a gap holding member (for convenience, indicated by reference numeral 40 in FIG. 2) for setting a predetermined gap between the charging roller and the photosensitive drum is provided.
[0041]
The developing devices 26M, 26Y, 26C, and 26Bk use a component-based developer in which toner and a carrier are mixed. Therefore, the developing devices 26M, 26Y, 26C, and 26Bk include photosensitive drums. The main part includes a developing roller facing 21M, 21Y, 21C, and 21Bk, a screw for conveying and stirring the developer, and a toner density sensor. The developing roller magnetic brush can be formed, and includes a rotatable outer sleeve and a magnet fixed inside. The toner is supplied from the toner supply device in accordance with the output of the toner density sensor.
[0042]
The toner has a binder resin, a colorant, and a charge control agent as main components, and is further added with other additives as needed. As specific examples of the binder resin, polystyrene, styrene-acrylate copolymer, polyester resin, and the like can be used. As a colorant (for example, yellow, magenta, cyan, and black) used for the toner, those known for toner are used.
The amount of the colorant is suitably from 0.1 to 15 parts by weight based on 100 parts by weight of the binder resin.
[0043]
Specific examples of the charge control agent include a nigrosine dye, a chromium-containing complex, a quaternary ammonium salt, and the like, which are used depending on the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight based on 100 parts by weight of the binder resin.
[0044]
It is advantageous to add a fluidity imparting agent to the toner particles. Examples of the fluidity-imparting agent include fine particles of a metal oxide such as silica, titania, and alumina, and those obtained by subjecting the fine particles to a surface treatment with a silane coupling agent, a titanate coupling agent, or the like, or polystyrene, polymethyl methacrylate, or polyfluorinated metal. Polymer particles such as vinylidene are used. The particle size of these fluidity-imparting agents is in the range of 0.01 to 3 μm. The addition amount of these fluidity-imparting agents is preferably in the range of 0.1 to 7.0 parts by weight based on 100 parts by weight of the toner particles.
[0045]
As a method for producing the toner for a two-component developer used in the developing device of the present embodiment, it can be produced by various known methods or a method combining them. For example, in the kneading and pulverizing method, a binder resin and a coloring material such as carbon black and necessary additives are dry-mixed, heated and kneaded with an extruder or a two-roll, three-roll, or the like, and then cooled and solidified. The toner is obtained by pulverizing with a pulverizer such as a jet mill and classifying with an airflow classifier. Further, a toner can be directly produced from a monomer, a colorant, and an additive by a suspension polymerization method or a non-aqueous dispersion polymerization method.
[0046]
As the carrier, a core material itself or a core material provided with a coating layer is generally used. The core material of the resin-coated carrier that can be used in the present embodiment is ferrite or magnetite. The particle size of the core material is suitably about 20 to 60 μm.
[0047]
Materials used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. As a method of forming the coating layer, a resin may be applied to the surface of the carrier core material particles by a spraying method, a dipping method, or the like, as in the related art.
[0048]
As shown in FIG. 2, each of the image forming devices 21M, 21Y, 21C, and 21Bk has a unit structure in which at least a photosensitive drum used as a latent image carrier and a charging device are housed together. It is used as a process cartridge that can be attached to and detached from. Each image forming unit, which is a process cartridge capable of forming an image of each color that can be attached to and detached from the housing, is provided with a positioning main reference portion 51 as a reference when being attached to and detached from the housing of the apparatus main body. When the positioning auxiliary reference portion 52 and the back side positioning auxiliary reference portion 53 are provided integrally with the bracket 50, and each image forming unit (corresponding to the configuration indicated by reference numerals 21M, 21Y, 21C, and 21Bk) is mounted on the apparatus main body. In addition, these reference portions ensure that each image forming unit can be positioned at a predetermined mounting position.
[0049]
The cleaning devices 28M, 28Y, 28C, and 28Bk are provided with a configuration for the photosensitive drums 25M, 25Y, 25C, and 25Bk, and a configuration for the charging devices 27M, 27Y, 17C, and 17Bk. The former configuration includes a cleaning brush (for convenience, indicated by reference numeral 28M1 in FIG. 2) and a cleaning blade (for convenience, indicated by reference numeral 28M2 in FIG. 2), and is scraped off by the cleaning blade 28M2. The removed toner is moved by a cleaning brush 28M1 to a screw auger 28M3 for toner conveyance.
[0050]
The cleaning device for the charging device (for convenience, indicated by reference numeral 270 in FIG. 2) includes the gap holding member 40 as well as the insulating resin 27M2 located on the chargeable material layer of the charging roller constituting the charging device. The roller itself has a scraping structure using an elastic body or a flexible fiber so as to adapt to the difference in diameter between the resin material portion 27M2 and the gap holding member 40. ing.
[0051]
The detailed configuration of the charging devices 27M, 27Y, 27C, and 27Bk is as follows.
As shown in FIG. 3, a charging device (for convenience, described using reference numeral 27M shown in FIG. 2) includes a core metal 27M1 formed of a conductive support and a resin material used as a chargeable material layer. It is composed of a layer 27M2 and a gap holding member 40.
Stainless steel is used for the core metal 27M1, and its diameter is selected to be about 6 to 10 mm, thereby preventing bending deformation when cutting or pressing against the photosensitive drum and obtaining processing accuracy. In this way, the charging device is prevented from becoming large and the mass from increasing.
[0052]
The resin material layer 27M2 used as the chargeable material layer has a thickness of 10 ⁶ -10 ⁹ A material having a volume resistance of Ωcm is selected. This is because if the resistance is too low, leakage of the charging bias tends to occur when there is a defect such as a pinhole in the photosensitive drum, and if the resistance is too high, the discharge does not sufficiently occur and a uniform charging potential is obtained. The reason is that you cannot do that.
[0053]
A desired volume resistance can be obtained by mixing a conductive material with a resin serving as a base material.
As the base resin, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, ABS (acrylonitrile-butadiene-styrene copolymer), and polycarbonate can be used. Since these base resins have good moldability, they can be easily formed.
[0054]
As the conductive material, an ion conductive material such as a polymer compound having a quaternary ammonium base is preferable. Examples of the polyolefin having a quaternary ammonium group include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-san vinyl acetate copolymer, ethylene-propylene Polyolefin such as copolymerization and ethylene-hexene copolymerization.
In the present embodiment, the polyolefin having a quaternary ammonium base has been exemplified, but a polymer compound other than the polyolefin having a quaternary ammonium base may be used as long as the object of the present invention is not contravened.
[0055]
The ionic conductive material is uniformly blended with the base resin by using means such as a biaxial kneader or a kneader. By subjecting the compounded material to injection molding or extrusion molding on a cored bar, it can be easily molded into a roller shape.
The compounding amount of the ion conductive material and the base resin is selected from 30 to 80 parts by weight based on 100 parts by weight of the base resin, and the thickness of the resin material layer 27M2 of the charging roller is selected from 1 to 3 mm. ing. This is because if the resin material layer 27M2 is too thin, molding is difficult and there is a problem in strength. If the resin material layer 27M2 is too thick, the charging roller becomes large, and the actual resistance of the resin material layer 27M2 increases. The reason is that the charging efficiency is reduced due to the increase in the charge efficiency.
The resin material layer 27M2 may be coated with a protective layer having a thickness of several tens of μm to which toner or the like does not easily adhere by coating or the like.
[0056]
The outer diameter of the resin material layer 27M2 can be adjusted by cutting, but a step 27M3 for attaching the gap holding member 40 to the longitudinal direction of the resin material layer 27M2, that is, the axial end of the charging roller (FIG. 4) is formed.
[0057]
The gap holding member 40 is a member for maintaining a charging gap between the photoconductor drum and the charging roller by being pressed against the surface of the photoconductor drum, and includes a PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer), A heat-shrinkable tube made of a fluororesin material such as FEP (tetrafluoroethylene-hexafluoropropylene copolymer) is used. The resin shrinks by being heated while being wound on the outer peripheral surface of the resin material layer 27M2. It is crimped on the surface of the material layer 27M2.
[0058]
Since the resin used for the gap holding member 40 is excellent in releasability, it is difficult for toner to be fixed. Further, by using an insulating fluororesin, the occurrence of discharge at the position of the gap holding member 40 can be eliminated. be able to. As a result, the amount of discharge products generated when a discharge occurs can be reduced, and the discharge products accumulate on the surface of the photoconductor drum, resulting in an increase in the coefficient of friction of the surface of the photoconductor drum. The adverse effect that the cleaning blade 28M2 on the cleaning device 28M side is caught can also be eliminated.
[0059]
These fluorine-based resin materials are difficult to adhere to the resin because of their excellent releasability, but can be fixed to the roller by using heat shrinkage without using an adhesive.
[0060]
The gap holding member 40 is applied outside the image area on the photosensitive drum 25M side in the longitudinal direction of the charging roller, that is, in the axial direction, so that a gap is formed between the resin material layer 27M2 of the charging roller and the photosensitive drum 25M. (Gap) can be formed.
In the present embodiment, the above-described maximum value of the gap is suppressed to 100 μm or less in order to obtain a uniform charged state without generating abnormal discharge. In order to set such a gap, the charging roller used as the photosensitive drum 25M and the charging device 27M is required to have high accuracy, and the roundness is set to 20 μm or less. By maintaining such processing accuracy and gap accuracy, it is possible to prevent the photosensitive layer from being damaged even when the charging roller is made of a resin material having high hardness and comes into contact with the organic photoreceptor. it can.
[0061]
The charging roller used as the charging device 27M can be interlocked with a gear (not shown) attached to the cored bar 27M1 by meshing with a gear formed on a flange on the photosensitive drum 25M side. It rotates at substantially the same speed as the drum 25M.
[0062]
On the other hand, the charging roller is provided with a non-slip portion as shown in FIGS.
In FIG. 4, in the axial direction of the charging roller (for convenience, a charging device is denoted by reference numeral 27M), a metal core is attached to the surface of a step 27M3 formed at an end corresponding to the outside of the image forming area of the photosensitive drum 25M. A plurality of grooves (denoted by 27P for convenience) having a depth of 10 to 100 μm are arranged side by side in parallel with the longitudinal direction (axial direction) of 27M1, and the grooves 27P are provided in the gap holding member 40 (see FIG. 3). ) To prevent slippage.
[0063]
In the configuration shown in FIG. 5, the groove (indicated by reference numeral 27P ′ for convenience) constituting the anti-slip portion has an inclination angle with respect to the axial direction of the core metal 27M1, and the depth is set to 10 to 100 μm. A plurality are arranged side by side. The inclination angle of the groove 27P 'is set to an angle at which the groove 27P' does not inadvertently expand in the width direction due to the rotational force of the charging roller 27M. Thereby, when the gap member is inadvertently extended in the width direction, the frictional resistance is not generated between the gap member and the wall surface of the step 27M3, so that the frictional heat is not generated due to the frictional resistance. Avoid changes. Further, the depth of the grooves 27P and 27P 'is set in consideration of preventing shear breakage of the gap member 40.
[0064]
When the non-slip portion is formed by a groove, the gap holding member 40 faces each other than the groove and the groove, so that the surface as shown in FIG. 7 which is a part of the cross section of the charging roller shown in FIG. Is uneven, but in the case of the groove 27P shown in FIG. 4, the surface unevenness appears parallel to the axis of the photosensitive drum 25M parallel to the cored bar 28M1, and the surface of the photosensitive drum 25M Although a regular change of the gap occurs in the circumferential direction, in the inclined groove 27P 'shown in FIG. 5, irregularities on the surface of the gap holding member 40 are not parallel in the axial direction of the photosensitive drum 25M. No significant change. Thereby, even when rotation unevenness occurs on the photosensitive drum 25M side, a substantially uniform charging gap can be maintained, and image deterioration due to charging unevenness can be prevented. Even in the case shown in FIG. 4, since the gap dimension is set to be equal to or smaller than the above-described maximum value, the image is naturally not deteriorated.
[0065]
As a configuration of the non-slip portion, as shown in FIG. 6, the surface roughness may be set in a region where the gap holding member 40 is located.
In the configuration shown in FIG. 6, the anti-slip portion has the surface roughness of the step 27M3 larger than that of the resin material layer 27M2 other than the step 27M3. In the present embodiment, the roughness (Ra) on the surface of the step 27M3 is reduced. It is set to 12.5a or more.
[0066]
Since the present embodiment is configured as described above, the gap member 30 provided on the charging roller 27M is integrated by being pressed against the resin material layer 27M2 by heat shrinkage. In addition, since it is loaded in the step 27M3 formed in the resin material layer 27M2, it is prevented from coming off the charging roller 27M.
[0067]
On the other hand, when the charging roller 27M rotates in conjunction with the photosensitive drum 25M, the gap holding member 40 is pressed against the surface of the photosensitive drum 25M, and the difference in diameter between the photosensitive drum 25M and the charging roller 27M. Due to the peripheral speed difference. For this reason, the gap holding member 40 slides with the resin material layer 27M2 of the charging roller 27M, but this slip is prevented by the groove 27P or 27 'provided in the step 27M3 and further by the surface roughness. Will be. As a result, thermal expansion of the gap holding member 40 due to frictional heat generated by slippage is prevented, so that a change in the gap size due to the thermal expansion, particularly a tendency of the gap to become large, is suppressed, and the gap size is increased. The abnormal discharge that occurs at the time can be prevented.
[0068]
In the present embodiment, since the photosensitive drum and the charging roller are arranged in one unit, the position of the photosensitive drum and the charging roller is determined in the unit, and by replacing the entire unit, There is no need to adjust the gap, and the user can easily change the gap. In the above-described embodiment, the description has been made of the unit in which the photosensitive drum, the charging roller, and the cleaning are integrated. However, the cleaning may be configured as another unit, and further, the development may be performed as a unit integrated with the photoconductor and the charging. You can also.
[0069]
The inventor conducted experiments on the state of an image under the following conditions.
The charging roller 27M is a resin composition (volume resistivity of 10%) obtained by mixing 60 parts by weight of an ionic conductive agent with 100 parts by weight of ABS resin as a resin material layer 27M2 on a core metal 27M1 made of stainless steel having a diameter of 8 mm. ⁶ Ωcm) by injection molding, and the surface was cut to a diameter of 12 mm. Here, grooves having a width of 8 mm were formed at both ends of the resin material layer 27M2.
The depth of the groove was 50 μm, and the surface roughness of this surface was Ra 12.5a, and grooves with a depth of 10 μm were formed at 2 mm intervals at an angle of 30 ° with respect to the roller rotation axis. Here, a PFA tube having a thickness of 100 μm was cut into a width of 8 mm and attached. The tube was shrunk by heating at 120 ° C. for 20 minutes.
[0070]
The charging roller 27M was set in a photoconductor unit (corresponding to a process cartridge) of a color printer manufactured by Ricoh "Ipsiocolor 8000", and a paper passing test was performed at a linear speed of the photoconductor of 125 mm / sec. The charging bias was a DC component of -700 V, the AC component was a sine wave having a peak-to-peak voltage of 2.2 kV and a frequency of 900 Hz.
[0071]
When a paper passing test was performed on 100,000 sheets under the above conditions, the image was good throughout the test, and no swelling was observed in the heat-shrinkable tube after 100,000 sheets.
[0072]
By the way, as a comparative example, an experiment was conducted under the following conditions in the case where no anti-slip portion was provided.
8 mm wide grooves were formed at both ends of the resin layer. The depth of the groove was 50 μm at the center and 1.5 mm at both ends, and the depth was 150 μm. A PFA tube having a thickness of 100 μm was cut into a width of 8 mm and attached.
[0073]
When a 100,000-sheet passing test was performed under the same conditions as those of the experimental example based on the present embodiment, fine dot-like stains began to be generated on a part of the image after about 80,000 sheets. Was.
When the charging device was checked, the center of the heat-shrinkable tube was bulging, and the gap between the charging roller and the photosensitive member was widened, causing abnormal discharge.
[0074]
【The invention's effect】
According to the first and second aspects of the present invention, since the gap holding member can be prevented from slipping, rotation of the gap member can be prevented. Therefore, thermal expansion of the gap holding member due to frictional heat generated when the gap member rotates. This prevents the change of the charging gap between the latent image carrier and the charging device set by the gap holding member, thereby preventing the occurrence of image defects due to abnormal discharge or the like.
[0075]
According to the third aspect of the present invention, by setting the surface roughness, it is possible to increase the frictional force with respect to the gap member and perform the slip prevention, thereby suppressing the occurrence of frictional heat tail due to the careless rotation of the gap member. Becomes possible.
[0076]
According to the fourth aspect of the present invention, by using a resin containing an ion conductive material for the chargeable material layer, the workability can be improved and the processing accuracy can be maintained, and abnormal discharge is less likely to occur due to the presence of the gap. Can be obtained.
[0077]
According to the fifth aspect of the present invention, since the gap holding member is made of the insulating resin material containing fluorine, the discharge in the gap holding member itself is suppressed and the generation of the discharge product is suppressed by suppressing the discharge. Therefore, it is possible to prevent the cleaning member from being entangled due to an increase in the friction coefficient due to the discharge product, thereby preventing deterioration of the cleaning characteristics.
[0078]
According to the sixth aspect of the present invention, the frictional force is reduced by a simple structure in which a part of the chargeable material layer is provided with a plurality of grooves parallel to the longitudinal direction of the metal core so that the gap member cuts into the groove. It is possible to prevent the gap from changing due to inadvertent rotation of the gap member. By defining the specific depth, the gap member can be maintained by preventing the shear fracture of the gap member.
[0079]
According to the seventh aspect of the present invention, similarly to the sixth aspect of the present invention, the frictional force can be increased by a simple configuration in which only a plurality of inclined grooves are provided so that the gap member cuts into the groove. It is possible to prevent a change in the gap due to inadvertent rotation of the member. In addition, since the groove is not parallel to the longitudinal direction of the latent image carrier due to the inclined groove, irregularities on the surface of the gap member facing the groove and other portions are not parallel to the longitudinal direction of the latent image carrier. Accordingly, it is possible to prevent non-uniformity of charging due to gap non-uniformity that occurs when parallel, and to improve image quality.
[0080]
According to the eighth aspect of the present invention, since the maximum gap between the latent image carrier and the charging device is set to 100 μm or less, the charging member used for the charging device adheres to the latent image carrier side. By setting the environment in which the toner is not contaminated and in which an abnormal discharge is unlikely to occur, uniform charging can be performed, so that deterioration of image quality can be prevented.
[0081]
According to the ninth aspect of the present invention, by superimposing and applying an AC voltage having a voltage equal to or more than twice the discharge start voltage, the charging potential is made uniform even with a gap change, and stability due to environmental change is obtained. Can be maintained.
[0082]
According to the tenth aspect of the present invention, by cleaning the gap member in addition to the chargeable material layer in the charging device, the toner adhering to the latent image carrier by the contact with the latent image carrier is reversed. The transfer prevents the gap from changing, and further prevents the charging potential from changing due to the adhesion of the toner, thereby maintaining a stable charging state.
[0083]
According to the eleventh aspect of the present invention, the process cartridge having a unit structure in which the latent image carrier and the charging device are collectively housed is detachably provided in the housing in which these devices are arranged. It is not necessary to adjust the gap between the body and the charging device on the housing side, and it is possible to improve maintainability.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus to which a charging device according to an embodiment of the present invention is applied.
FIG. 2 is a schematic diagram for explaining a configuration of a process cartridge constituting an image forming apparatus including the charging device shown in FIG.
FIG. 3 is a schematic diagram illustrating a configuration of a charging roller used as a charging device.
FIG. 4 is a schematic diagram illustrating an example of a configuration of a main part of the charging roller illustrated in FIG. 3;
FIG. 5 is a schematic diagram showing another example of a main configuration of the charging roller shown in FIG. 3;
FIG. 6 is a schematic diagram showing another example of the configuration of the main part of the charging roller shown in FIG. 3;
FIG. 7 is a schematic diagram showing a part of a cross section of the charging roller shown in FIG.
[Explanation of symbols]
20 Image forming apparatus
27M charging device
27M1 cored bar
27M2 Chargeable resin material layer
27M3 step
27P groove
27P 'Inclined groove
40 Gap holding member

Claims (11)

A gap holding member capable of forming a chargeable material layer on the outer peripheral surface of the core metal, forming a gap by being wound on the surface of the chargeable material layer, projecting from the surface of the material layer, and contacting a mating side. In a charging device using a charging roller provided with
A charging device, wherein a part of the surface of the chargeable material layer is configured as a non-slip portion. The charging device according to claim 1,
The charging device, wherein the non-slip portion includes at least a region where the gap holding member is located. The charging device according to claim 1, wherein
A charging device, wherein the surface roughness of a part of the surface of the material layer where the gap holding member is located is larger than the surface of the material layer. The charging device according to claim 1, wherein:
A charging device characterized in that a resin material containing an ion conductive material is used for the chargeable material layer. The charging device according to claim 1, wherein:
The charging device, wherein the gap holding member is made of an insulating material containing fluorine. The charging device according to any one of claims 1 to 5,
A charging device, wherein a plurality of grooves having a depth of 10 to 1000 (μm) parallel to the longitudinal direction of the cored bar are formed in a part of the material layer where the gap holding member is located. The charging device according to any one of claims 1 to 5,
A plurality of grooves each having a depth of 10 to 1000 (μm) having an inclination angle with respect to a longitudinal direction of the cored bar are formed in a part of the material layer where the gap holding member is located. apparatus. An image forming apparatus using the charging device according to claim 1, wherein a gap between the gap holding member and the latent image carrier is set to 100 μm or less. The image forming apparatus according to claim 8,
The charging process is performed by superimposing and applying an AC voltage having a peak-to-peak voltage that is at least twice the discharge starting voltage between the chargeable material layer and the latent image carrier in the charging device. Image forming apparatus. The image forming apparatus according to claim 8, wherein
The charging device is provided with a cleaning member for cleaning the chargeable material layer, and the cleaning member has a configuration capable of forming a layer including the gap holding member in a width direction of the material layer. Image forming apparatus. The image forming apparatus according to any one of claims 8 to 10,
At least the latent image carrier and the charging device are collectively accommodated and housed in a unit structure, and a process cartridge detachable from a housing in which the latent image carrier and the charging device are arranged is provided. Image forming apparatus.

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